What do polar bears eat?
The polar bear's main prey is the ringed seal. Polar bears usually hunt ringed seals by waiting for them to breathe at openings in the ice (leads) or at breathing holes. Polar bears will also stalk seals that are hauled out on top of the ice.
In fall, a seal cuts ten to fifteen breathing holes (known as aglus by Canadian Inuit) in the ice using the sharp claws on its foreflippers. It keeps the breathing holes open all winter long, even in ice up to six feet (~two meters) thick. Seals surface about every five to fifteen minutes at one of these breathing holes. Seals also use air pockets trapped under the ice when available.
Polar bears locate breathing holes with their powerful sense of smell and lie in wait for the seals to rise. Polar bears have to be smart and patient because the wait can be long—from hours to days.
Seal stalking. Bears also stalk ringed seals that are basking on the ice by taking advantage of their sleep-wake rhythms. The bear crawls slowly forward and freezes in place when the animal raises its head. At about 20 feet from the seal, the bear uses its explosive speed to pounce, killing the seal before it can escape back into the sea.
- Ringed seals are the most abundant seal in the Arctic. They live in water and use land-fast, solid ice, and ice floes for resting, molting, and giving birth.
- Adult ringed seals have a thick layer of blubber and reach an average length and weight of 4.1 feet and 150 pounds. Their backs are dark and spotted with cream-colored rings. Underneath, their coats are white to creamy yellow.
- Seal pups are typically born in snow dens on land-fast ice in March and April. Their mother nurses them for about two months and pups learn to swim and hunt as the ice breaks up in early summer. The seal pupping season is a time of plenty for polar bears: naive young pups make easy prey.
- A warming Arctic also threatens ringed seals. Loss of ice limits their distribution, rain events can collapse lairs, and low snow years can mean seal pups are born in the open, where they become easy prey for arctic foxes, several bird species, and polar bears. In western Svalbard, changes in sea ice extent and snow cover have led to reproductive failure for ringed seals in some areas.
Ice is a must. Both polar bears and ringed seals depend on it.
- Polar bears' lives are a cycle of feasting and fasting. When hunting is good and a polar bear is in good body condition, the bear will eat only the seal's blubber and skin. A polar bear can eat 100 pounds of blubber in a single sitting! Other bears devour the remains, as do arctic foxes, gulls, and even ravens.
- Scientists have found that when polar bears dine exclusively on seal fat, their cholesterol levels drop lower than those of fasting bears likely due to the protective quality of the omega-3 fatty acids found in the seals.
- In summer, when ice floes retreat, most polar bears follow the ice—sometimes traveling hundreds of miles—to stay with their food source.
- Polar bears who come ashore face lean times in most of the Arctic. Terrestrial sources of food simply lack the fat content and calories of the polar bear’s preferred prey, and catching seals in open water is no easy task.
Other foods. While polar bears have evolved as a highly specialized predator of ice seals, they are always alert to other food sources—including vegetation, geese, bird eggs, and even the occasional small mammal. Although individual bears may benefit from eating these alternative foods in places where they occur, there is yet no evidence they could provide enough calories, in the right form, to sustain polar bears at the population level. Increased polar bear use of terrestrial foods would also have negative impacts on those species and others who rely on them for survival—the barren ground grizzly, arctic fox, wolves, and several scavengers and birds of prey.
Polar bears also occasionally feed on other arctic marine mammals, including bowhead whale remains, walrus, and narwhal. Beluga whale or narwhal that become trapped in a savsatt—a small opening in pack ice—become easy prey for the bears. And whale carcasses on the shore or those frozen in the sea ice offer a bonanza. However, none of these alternative marine foods are available on a predictable enough basis to offset the possible loss of ringed and bearded seals.
Bounty. Alaskan marine biologist Lloyd Lowrey observed a group of bears capture about 40 beluga whales at a savsatt in the northern Bering Sea. And in 1999, 13 bears harvested beluga whales trapped in a savsatt near Canada's Ellesmere Island.
Dining etiquette. Russian scientist Nikita Ovsyanikov once observed about 100 polar bears around a gray whale carcass. He's also seen fourteen polar bears eating shoulder-to-shoulder at a single walrus carcass. Our own scientists routinely see groups of three or four male polar bears sharing a seal carcass on the shores of Hudson Bay during our fall survey efforts.
According to Ovsyanikov, although one bear may own a large carcass, he won't object to sharing if his guests beg properly. Begging involves a submissive, low-to-the-ground approach, followed by a slow circle around the carcass, and touching the nose of the bear in charge.